The Group of Eight leaders who are meeting in Sea Island, Ga., this week face a historic test of leadership. In the wake of the Madrid bombings and warnings that al Qaeda is planning attacks in the United States, this summit must produce more than the usual photo opportunities and joint statements. Its success should be measured in large part by whether the G-8 leaders take concrete and urgent steps to reduce the risk of catastrophic terrorism.

Unfortunately, the risk that terrorists could acquire and use nuclear, chemical or biological weapons is all too real. Over time, and without our decisive intervention, al Qaeda could become the world's 10th nuclear power. The terrorist organization has made several attempts to acquire uranium that could be used to make a crude nuclear device, and documents discovered at an al Qaeda safe house in 2001 showed an understanding of nuclear weapons design. The hardest part for the terrorists is getting the plutonium or highly enriched uranium necessary to build a bomb. Making that impossible should be our goal.

At their 2002 summit the G-8 leaders launched a Global Partnership Against the Spread of Weapons and Materials of Mass Destruction, in which they pledged $20 billion -- $10 billion from the United States, $10 billion from others -- over 10 years to reduce the risk of catastrophic terrorism. Two years after this global security breakthrough, they are $3 billion short of their pledges, and only a tiny fraction of the $17 billion pledged has been appropriated for programs. Disputes between Russia and donor countries over tax issues, liability questions and site access have slowed implementation.

As a result, less than one-quarter of Russia's nuclear bomb-making materials -- hundreds of metric tons of plutonium and highly enriched uranium (HEU) -- has been adequately secured against theft or diversion. Globally, there are still more than 130 nuclear research reactors and other facilities in 40 countries using or storing weapons-usable HEU, and many of these facilities have only the most rudimentary security measures.

The problem is not confined to unsecured nuclear materials. Millions of portable artillery shells and hundreds of missile warheads filled with deadly nerve agents await destruction at dilapidated facilities in Russia. Construction of a U.S.-funded destruction plant was delayed for three years by political and compliance disputes, and current destruction plans will take more than a decade to implement. In the meantime, one stolen shell could be used to kill tens of thousands of people in Washington, New York, London, Paris, Tokyo or Moscow.

In addition, Russian military and civilian research facilities still have deadly pathogen collections; we don't know exactly what kind they are, how many there are or how secure they are. Thousands of former weapons scientists and workers in Russia remain underpaid or unemployed, making them more vulnerable targets for recruitment by terrorist organizations.

Although significant work has begun in all these areas, projected completion dates stretch into the next decade and beyond. Given the concerted efforts of al Qaeda and possibly other terrorist groups to acquire nuclear, biological and chemical weapons, there is now a dangerous gap between the pace of our progress and the urgency of the threat. We are not accelerating these programs as if our lives depended on it. They do.

There are at least 10 steps that G-8 leaders could take at Sea Island to give us a chance of winning this race against terrorism:

1. Appoint a senior official in each government, with direct access to the president or prime minister, who is responsible and accountable for ensuring that terrorists do not acquire weapons of mass destruction. Empower this senior official to eliminate all obstacles to cooperation as quickly as possible.

2. Announce an intention to increase pledges to the global partnership above the $20 billion goal. This goal should be treated as a floor, not a ceiling.

3. Expand the global partnership to include all nations with weapons capability and weapons materials, specifically Pakistan, India, Israel and China.

4. Accelerate efforts to consolidate and secure weapons-usable nuclear materials worldwide.

5. Accelerate the demilitarization of Russia's stockpile of 40,000 tons of chemical agents and strengthen the security of all chemical weapon stocks awaiting destruction in Russia.

6. Take immediate steps to account for and secure dangerous biological pathogen collections across Russia and the former Soviet Union.

7. Initiate a global effort to combat both infectious diseases and biological terrorism.

8. Expand efforts to employ former weapons scientists and personnel in the former Soviet Union.

9. Presidents Bush and Putin should pledge to bilaterally increase the transparency, safety and security of all tactical nuclear weapons in and around Europe.

10. Bush and Putin should also announce a new initiative to make U.S. and Russian biological defense research efforts bilaterally transparent as a confidence-building measure to enable greater cooperation in the biological arena.

This is not a list of impossible dreams; these are global security imperatives. Taking these steps will require the personal commitment and persistent action of the presidents of the United States and Russia, the leaders of the G-8 and other countries around the globe. The clock is ticking.

Sam Nunn, a former Democratic senator from Georgia, is co-chairman of the Nuclear Threat Initiative. Michele Flournoy is a senior advisor at the Center for Strategic and International Studies and co-director of the Strengthening the Global Partnership project.